Semiconductor light emitting devices, such as laser diodes (LD) and LEDs are widely used as high efficiency direct electric modulation light sources for testing of various passive and active optical components, as well as for illumination. A LED usually is a large spectral bandwidth Lambertian source with a broad emitting area, which makes it difficult to efficiently couple the light radiation to relatively small cross section waveguide structures, such as fibers.
Traditional methods of coupling a light into the fiber use micro-lens components positioned between the light source and the fiber. Typical examples of this type of system are shown in U.S. Pat. No. 5,215,489 entitled METHOD OF MAKING AN OPTICAL SEMICONDUCTOR MODULE, which issued on Jun. 1, 1993 to Nakamura, Canadian patent No 2,159,136 entitled OPTICAL FIBER ASSEMBLY, which issued on Jul. 3, 2001 to Takahashi and Canadian Patent No 1,113,762 entitled OPTICAL COUPLER FOR CONNECTING A LIGHT SOURCE TO AN OPTICAL TRANSMISSION LINE, which issued on Dec. 8, 1981 to Balliet. Thus, light emerging from the light source passes through a micro-lens system and traverses several optical surfaces (between media with different refractive indices), which introduces undesirable reflection losses. In addition, the required micro-optical components, and the need for fine micro positioning of these elements, significantly decrease the performance of the device and increase its cost, particularly for small diameter components such as single mode fibers, etc.
Different approaches are known for addressing the problem of increasing the coupling efficiency between the LED and optical fiber. For example, U.S. Pat. No. 4,376,946 entitled SUPERLUMINESCENT LED WITH EFFICIENT COUPLING TO OPTICAL WAVEGUIDE, which issued on Mar. 15, 1983 to Kaminow et al., teaches a method of coupling a super luminescent LED having lateral confinement of the light in the junction plane, to an optical waveguide. According to Kaminow et al., a special waveguide defined in the LED by different refractive index semiconductor layers is constructed to have an effective numerical aperture equal to the numerical aperture of the optical waveguide. As a result, photons emitted by the LED can be effectively guided into the optical waveguide. The device of Kaminow et al. suffers the limitation that it requires a special (costly) superluminescent LED having a spectral bandwidth, which is narrower than an ordinary LED's bandwidth. However, often a conventional broad bandwidth LED's light is preferable for utilization in optical testing equipment.
U.S. Pat. No. 4,826,272 entitled MEANS FOR COUPLING AN OPTICAL FIBER TO AN OPTO-ELECTRONIC DEVICE, which issued on May 2, 1989 to Pimpinella et al., teaches a system for coupling an optical fiber and semiconductor device by inserting the fiber and light source into “wells” formed in a supporting body. Precise and expensive technological processes such as photolithography and selective etching must be used for the manufacturing of this structure.
U.S. Pat. No. 4,170,399 entitled LED FIBER OPTIC CONNECTOR, which issued on Oct. 9, 1979 to Hansen et al., teaches an improved connector scheme for coupling the output of a LED to an optical fiber. In this case, a large-diameter optical fiber having a wide angle of acceptance is placed in abutting position against one side surface of the LED. The diameter of the fiber exceeds the thickness of the LED and the fiber has a wide angle of acceptance (about 64 degrees) that encompasses substantially all the light emitted through the surface of the LED. Accordingly, this approach is not suitable for use with standard optical fibers, which are typically much narrower in diameter and have a much narrower angle of acceptance (25–30 degrees).
Accordingly a method of optically connecting a standard light emitting device to an optical waveguide structure that is both efficient and inexpensive, remains highly desirable.